Stable,Wavelength‐Tunable Fluorescent Dyes in the NIR‐II Region for In Vivo High‐Contrast Bioimaging and Multiplexed Biosensing

Small‐molecule organic fluorophores, spectrally active in the 900–1700 nm region, with tunable wavelength and sensing properties are sought‐after for in vivo optical imaging and biosensing. A panel of fluorescent dyes ( CX ) has been developed to meet this challenge. CX dyes exhibit the wavelength tunability of cyanine dyes and have a rigidified polymethine chain to guarantee their stability. They are chemo‐ and photo‐stable in an aqueous environment and have tunable optical properties with maximal absorbing/emitting wavelength at 1089/1140 nm. They show great potential in high‐contrast in vivo bioimaging and multicolor detection with negligible optical cross talk. Förster resonance energy transfer (FRET) between CX dyes was demonstrated in deep tissue, providing an approach for monitoring drug‐induced hepatotoxicity by detection of OONO^?. This report presents a series of NIR‐II dyes with promising spectroscopic properties for high‐contrast bioimaging and multiplexed biosensing.     

Expanding the Arsenal of PtIV Anticancer Agents: Multi‐action PtIV Anticancer Agents with Bioactive Ligands Possessing a Hydroxy Functional Group

Most multi‐action Pt^IV prodrugs have bioactive ligands containing carboxylates. This is probably due to the ease of carboxylating the OH axial ligands and because following reduction, the active drug is released. A major challenge is to expand the arsenal of bioactive ligands to include those without carboxylates. We describe a general approach for synthesis of Pt^IV prodrugs that release drugs with OH groups. We linked the OH groups of gemcitabine (Gem), paclitaxel (Tax), and estramustine (EM) to the Pt^IV derivative of cisplatin by a carbonate bridge. Following reduction, the axial ligands lost CO₂, rapidly generating the active drugs. In contrast, succinate‐linked drugs did not readily release the free drugs. The carbonate‐bridged ctc‐[Pt(NH₃)₂(PhB)(Gem‐Carb)Cl₂] was significantly more cytotoxic than the succinate‐bridged ctc‐[Pt(NH₃)₂(PhB)(Gem‐Suc)Cl₂], and more potent and less toxic than gemcitabine, cisplatin, and co‐administration of cisplatin and gemcitabine.     

Assembly of a Highly Stable Luminescent Zn5 Cluster and Application to Bio‐Imaging

The assembly sequence of the coordination cluster [Zn₅(H₂Lⁿ)₆](NO₃)₄]⋅8 H₂O⋅2 CH₃OH ( Zn₅ , H₃Lⁿ=(1,2‐bis(benzo[d]imidazol‐2‐yl)‐ethenol) involves in situ dehydration of 1,2‐bis(benzo[d]imidazol‐2‐yl)‐1,2‐ethanediol (H₄L) through the formation of the [Zn(H₃L)₂]⁺ monomer, dimerization to [Zn₂(H₃L)₂]⁺, dehydration of the ligand to [Zn₂(H₂Lⁿ)₂]⁺, and the final formation of the pentanuclear cluster. The cluster has the following special characteristics: 1) high stability in both refluxing 37 % HCl and 27 % NH₃, 2) low cytotoxicity, and 3) pH‐sensitive fluorescence in the visible‐to‐near‐infrared (Vis/NIR) region in the solid state and in solution. We have applied it as a fluorescent probe both in vivo and in vitro. Its H‐bonding ability is the key to its affinity and selectivity for imaging lysosomes in HeLa cells and tumors in male BALB/C mice. It provides a new type of sensitive and biocompatible fluorescent probe for detecting small tumors (13.5 mm³).     

A General Strategy for Development of Near‐Infrared Fluorescent Probes for Bioimaging

Near‐infrared (NIR) fluorescent dyes with favorable photophysical properties are highly useful for bioimaging, but such dyes are still rare. The development of a unique class of NIR dyes via modifying the rhodol scaffold with fused tetrahydroquinoxaline rings is described. These new dyes showed large Stokes shifts (>110 nm). Among them, WR3, WR4, WR5, and WR6 displayed high fluorescence quantum yields and excellent photostability in aqueous solutions. Moreover, their fluorescence properties were tunable by easy modifications on the phenolic hydroxy group. Based on WR6, two NIR fluorescent turn‐on probes, WSP‐NIR and SeSP‐NIR, were devised for the detection of H₂S. The probe SeSP‐NIR was applied in visualizing intracellular H₂S. These dyes are expected to be useful fluorophore scaffolds in the development of new NIR probes for bioimaging.     

Glucose Biosensor Using Glucose Oxidase and Electrospun Mn2O3‐Ag Nanofibers

The highly porous Mn₂O₃‐Ag nanofibers were fabricated by a facile two‐step procedure (electrospinning and calcination). The structure and composition of the Mn₂O₃‐Ag nanofibers were characterized by SEM, TEM, XRD, EDX and SAED. The as‐prepared Mn₂O₃‐Ag nanofibers were then employed as the immobilization matrix for glucose oxidase (GOD) to construct an amperometric glucose biosensor. The biosensor shows fast response to glucose, high sensitivity (40.60 µA mM^?1 cm^?2), low detection limit (1.73 µM at S/N=3), low K_m,app value and excellent selectivity. These results indicate that the novel Mn₂O₃‐Ag nanfibers‐GOD composite has great potential application in oxygen‐reduction based glucose biosensing.     

Direct Electrochemistry of Glucose Oxidase at Reduced Graphene Oxide and β‐Cyclodextrin Composite Modified Electrode and Application for Glucose Biosensing

A simple glucose biosensor has been developed based on direct electrochemistry of glucose oxidase (GOx) immobilized on the reduced graphene oxide (RGO) and β‐cyclodextrin (CD) composite. A well‐defined redox couple of GOx appears with a formal potential of ～?0.459 V at RGO/CD composite. A heterogeneous electron transfer rate constant (K_s) has been calculated for GOx at RGO/CD as 3.8 s^?1. The fabricated biosensor displays a wide response to glucose in the linear concentrations range from 50 µM to 3.0 mM. The sensitivity and limit of detection of the biosensor is estimated as 59.74 µA mM^?1 cm^?2 and 12 µM, respectively.     

Atypical Lone Pair–π Interaction with Quinone Methides in a Series of Imido‐Ferrociphenol Anticancer Drug Candidates

Ferrociphenols, especially those possessing a heterocycle at the terminus of an aliphatic chain, display strong anticancer activity through a novel redox mechanism that generates active metabolites such as quinone methides (QMs). X‐ray crystallography and UV/Vis spectroscopy reveal that the specific lone pair (lp)–π interaction between a carbonyl group of the imide and the quinone motif of the QM plays an important role in the exceptional cytotoxic behaviour of their imido‐ferrociphenol precursors. This intramolecular lp–π interaction markedly enhanced the stability of the QMs and lowered the pK_a values of the corresponding phenol/phenolate couples. As the first example of such a non‐covalent interaction that stabilizes QMs remotely, it not only expands the scope of the lp–π interaction in supramolecular chemistry, but also represents a new mode of stabilization of a QM. This unprecedented application of lp–π interactions in imido‐ferrociphenol anticancer drug candidates may also have great potential in drug discovery and organocatalyst design.     

Protein‐Specific,Multicolor and 3D STED Imaging in Cells with DNA‐Labeled Antibodies

Photobleaching is a major challenge in fluorescence microscopy, in particular if high excitation light intensities are used. Signal‐to‐noise and spatial resolution may be compromised, which limits the amount of information that can be extracted from an image. Photobleaching can be bypassed by using exchangeable labels, which transiently bind to and dissociate from a target, thereby replenishing the destroyed labels with intact ones from a reservoir. Here, we demonstrate confocal and STED microscopy with short, fluorophore‐labeled oligonucleotides that transiently bind to complementary oligonucleotides attached to protein‐specific antibodies. The constant exchange of fluorophore labels in DNA‐based STED imaging bypasses photobleaching that occurs with covalent labels. We show that this concept is suitable for targeted, two‐color STED imaging of whole cells.     

Synthesis of a Fluorescent Analogue of Paclitaxel That Selectively Binds Microtubules and Sensitively Detects Efflux by P‐Glycoprotein

The anticancer drug paclitaxel (Taxol) exhibits paradoxical and poorly understood effects against slow‐growing tumors. To investigate its biological activity, fluorophores such as Oregon Green have been linked to this drug. However, this modification increases its polarity by approximately 1000‐fold and reduces the toxicity of Taxol towards cancer cell lines by over 200‐fold. To construct more drug‐like fluorescent probes suitable for imaging by confocal microscopy and analysis by flow cytometry, we synthesized derivatives of Taxol linked to the drug‐like fluorophore Pacific Blue (PB). We found that PB‐Gly‐Taxol bound the target protein β‐tubulin with both high affinity in vitro and high specificity in living cells, exhibited substantial cytotoxicity towards HeLa cells, and was a highly sensitive substrate of the multidrug resistance transporter P‐glycoprotein (P‐gp).     

Direct Electrochemistry of Glucose Oxidase on Nail‐like Carbon and Its Biosensing for Glucose

Nail‐like carbon (NLC) was synthesized by a simple hydrothermal method. It was the first time that a novel electrochemical biosensing of glucose was explored based on the glucose oxidase (GOx)‐NLC‐chitosan (CHIT) glassy carbon electrode. Morphology and structure of NLC were characterized by scanning electron microscope; meanwhile the chemical composition was determined by X‐ray diffraction and energy dispersive X‐ray spectroscopy. The cyclic voltammetry of immobilized GOx showed a pair of quasireversible redox peaks with the formal potential (E°′) of ?0.458 V and the peak‐to‐peak potential separation was 47 mV at a scan rate of 100 mV s^?1. The present biosensor has a linear range of glucose from 0.02 to 1.84 mM (correlation coefficient of 0.9991) and detection limit of 0.01 mM (S/N=3). Compared with the previous reports based on the carbon material biosensor, it has a high sensitivity of 165.5 μA mM^?1 cm^?2 and low apparent Michaelis–Menten constant of 0.506 mM. Thus, the NLC may have potential applications in the field of bioelectrochemistry, bioelectronics and biofuels.     

Development of Amperometric Glucose Biosensor Based on Reconstitution of Glucose Oxidase on Polymeric 3‐Aminophenyl Boronic Acid Monolayer

An amperometric biosensor for determining glucose based on deflavination of the enzyme glucose oxidase and subsequent reconstitution of the apo‐protein with a complexed flavin adenine dinucleotide (FAD) monolayer is described. The GOx‐reconstituted electrode exhibited excellent electrocatalytic activities towards the reduction and oxidation of hydrogen peroxide as well. The prepared biosensor showed an excellent performance for glucose at +0.5 V with a high sensitivity (5.94 μA/mM) and relatively good response time (～12 s) in a wide concentration range of 1–17 mM (correlation coefficient of 0.9998). The applicability to blood analysis was also evaluated.     

A Novel Process for the Fabrication of a Silver‐Nanoparticle‐Modified Electrode and Its Application in Nonenzymatic Glucose Sensing

In this work, we present a novel process for fabrication of a silver‐nanoparticle‐modified electrode using silver ion implantation. This method is facile, low‐cost and environmental friendly without the use of any other chemicals. The obtained AgNPs on the electrode surface, which were free from any reagents surrounding or binding to them, showed prominent electrocatalytic activity towards the oxidation of glucose, leading to a nonenzymatic glucose sensor with a wide linear range and a detection limit of 0.5 µM. In addition, the modified electrode also exhibited acceptable reproducibility and long‐term stability.     

Direct Electrochemistry of Glucose Oxidase Immobilized at a Novel Composite Material β‐Cyclodextrin/poly(4‐aminothiophenol)/Au Nanoparticle Modified Electrode

A novel complex material was fabricated by three steps. In the first step, gold nanoparticle (Au_nano) was prepared with the method of chemistry and dialysis. In the second step, 4‐aminothiophenol (AT) was encapsulated in the cavity of β‐cyclodextrin and formed inclusion complex, cyclodextrin/4‐aminothiophenol (CD/AT). And then inclusion complex was adsorbed to the surface of Au_nano based on the bond of Au‐S interaction. In the last step, a complex material, cyclodextrin/poly(4‐aminothiophenol)‐Au nanoparticles (CD/PAT‐Au_nano) was obtained by the polymerizing in the acid solution initiated by chlorauric acid. The CD/PAT‐Au_nano has spherical nanostructure with the average diameter of 55 nm. Glucose oxidase (GOx) was anchored with this complex material and direct electrochemistry of GOx was achieved. A couple of stable and well‐defined redox peaks were observed with the formal potential (E^0′) of ‐0.488 V (vs. SCE) in a pH 6.98 buffer solution. The GOx modified electrode also exhibited an excellent electrocatalytic activity to the reduction of glucose, a linearity range for determination of glucose is from 0.25 mM to 16.0 mM with a detection limit of 0.09 mM (S/N = 3). This protocol had potential application to fabricate the third‐generation biosensor.     

β‐AgVO3 Nanorods as Peroxidase Mimetic for Colorimetric Determination of Glucose

β‐AgVO₃ nanorods have been demonstrated to exhibit intrinsic peroxidase‐like activity. The oxidation of glucose can be catalyzed by glucose oxidase (GOx ) to generate H₂O₂ in the presence of O₂ . The β‐AgVO₃ nanorods can catalytically oxidize peroxidase substrates including o‐phenylenediamine (OPD ), 3,3′,5,5′‐tetramethylbenzidine (TMB ), and diammonium 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonate) (ABTS ) by H₂O₂ to produce typical color reactions: OPD from colorless to orange, TMB from colorless to blue, and ABTS from colorless to green. The catalyzed reaction by the β‐AgVO₃ nanorods was found to follow the characteristic Michaelis–Menten kinetics. Compared with horseradish peroxidase and AgVO₃ nanobelts, β‐AgVO₃ nanorods showed a higher affinity for TMB with a lower Michaelis–Menten constant (K _m) value (0.04118 mM ) at the optimal condition. Taking advantage of their high catalytic activity, the as‐synthesized β‐AgVO₃ nanorods were utilized to develop a colorimetric sensor for the determination of glucose. The linear range for glucose was 1.25–60 μM with the lower detection limit of 0.5 μM . The simple and sensitive GOx ‐β–AgVO₃ nanorods–TMB sensing system shows great promise for applications in the pharmaceutical, clinical, and biosensor detection of glucose.